Research and analysis

Kent and South London water situation: April 2024 summary

Updated 15 May 2024

Applies to England

• Publication for Northern Ireland
• Publication for Scotland
• Publication for Wales

1. Summary

The whole of the Kent and South London area received 143% of the long-term average rainfall during April. Rainfall received across catchments in the area ranged from above normal to notably high for this time of the year.  Across the assessment areas, soil moisture deficits were consistently below and mostly three times below the long-term average for April. Monthly mean river flows for April ranged from normal to exceptionally high in the Kent and South London area. Groundwater levels ranged from above normal to exceptionally high in the Chalk aquifers and were exceptionally high in the Lower Greensand aquifers at Riverhead. Levels at the five water company reservoirs ranged from normal exceptionally high in the Kent and South London area.   

2. Rainfall 

The whole of the Kent and South London (KSL) area received 143% of the long-term average (LTA) rainfall during April. Rainfall received across catchments in the area ranged from above normal to notably high. All catchments in the west of KSL received rainfall above normal, while catchments in the east received notably high amounts of rain for this time of year. The highest daily rainfall total of 30.4mm for April occurred on the twenty seventh day of the month and was recorded at Orpington PS rain gauge in the Darent catchment. Days 1, 2, 3 and 26 had the next highest daily rainfall totals that ranged from 28.4mm to 10.6mm. During the previous three months, which spanned from February to April, rainfall was exceptionally high across all catchments. In the previous 6 months, spanning November to April, rainfall across the Kent and South London area was exceptionally high in all catchments except for Sheppey in the north. The last twelve months saw rainfall that was exceptionally high in catchments in the south and notably high and above normal in catchments in the north. KSL area saw the sixth wettest six months since records began in 1872. The last 3 months saw catchments in the top ten wettest 3 months; Medway, Dover chalk and Upper Mole held the second wettest 3 months with 312.6mm, 348.6mm and 324mm rainfall, respectively. The last 6 months saw Dover chalk had the wettest 6 months with 763.3 mm rainfall. The last 12 months also saw Dover chalk catchment hold the 2nd wettest 12 months with 1214.4 mm rainfall 

3. Soil moisture deficit and recharge  

Across the assessment areas, soil moisture deficits (SMDs) were consistently below and mostly three times below the long-term average (LTA) for the month of April. Compared to the LTA for the month of April, SMDs continue to be considerably lower, meaning that by this month, soils were wetter than they would be under average conditions; although, when compared to March, SMDs increased marginally. This is consistent with the amount of effective rainfall KSL received this month, which was 167% of the LTA across the whole area, dryer than March. Aquifers continue to remain highly responsive, and depending on their intensity, rainfall events are resulting in groundwater levels rising after relatively short time periods. 

4. River flows 

Monthly mean river flows (MMFs) for March ranged from normal to exceptionally high.  The majority of these were notably high with two flow sites, Dour at Crabble and Darent at Hawley being exceptionally high, Medway at Teston, Rother at Udiam and Teise at Stonebridge were above normal, and Ravensbourne at Catford was the only flow site that was in the normal category. The key flow site with the highest MMF banding was Dour at Crabble which saw 205% of the LTA for the month of April. The lowest percentage of LTA monthly mean river flow was observed at Ravensbourne at Catford, which recorded 105% of the LTA. 

5. Groundwater levels   

Groundwater levels in the Chalk across KSL area in April 2024 were exceptionally high at Wolverton and Little Bucket. Riddles Lane and Fleete Reservoir, Sweeps Lane and Chipstead in the north were notably high for this time of year.  Groundwater levels in the Greensand at Riverhead were exceptionally high.  Due to the continued above average effective rainfall and low SMDs across the KSL area, groundwater levels in the Chalk and Lower Greensand aquifers remain high throughout April. The majority of groundwater sites show a slight decrease in levels with the exception of Riddles Lane and Sweeps Lane which saw a slight increase. Aquifers continue to be highly responsive, and spells of heavy, intensive rainfall would have the potential for groundwater to rise more rapidly, within relatively short time periods. During the next month, we expect periods of weather with sunnier and warmer conditions, alongside the onset of vegetation growth. As a result of these conditions, it is likely, effective rainfall/aquifer recharge will diminish, which in turn will lead to all monitoring locations indicating a fall in groundwater levels and the fall will continue until the onset of the next recharge season.  

Due to the rise in groundwater levels in East Surrey and South London that occurred since February, a flood alert for groundwater flooding was issued on the 6 of March, and it is still in effect for South East London area. The flood alert for the area of East Kent issued in December 2023 is also still in effect. Given that groundwater levels in most areas are falling and that the start of groundwater levels to fall in the remaining areas is imminent, flood alerts are currently under review and are likely to be removed within the month of May. 

6. Reservoir stocks  

At the end of April, reservoir levels were normal at Darwell at 95% and Powdermill at 100%, above normal at Weirwood with 100% and exceptionally high for this time of year at Bewl and Bough Beech both at 100%.   Most of the levels in the reservoirs remained unchanged throughout the month of April, however water levels in Darwell reservoir have minimally decreased and levels in Powdermill had a slight decrease before returning to 100% at the end of the month. 

7. Environmental impact   

Five flood alerts were issued throughout April on 3, 8, and 28 of the month. The groundwater flooding alert issued for South London East in March 2024 and the groundwater flooding alert for East Kent has remained in force. 

Author: Groundwater and Hydrology Team, ksl.gwh@environment-agency.gov.uk 

Contact details: 0370 850 6506 

All data are provisional and may be subject to revision. The views expressed in this document are not necessarily those of the Environment Agency. Its officers, servants or agents accept no liability for any loss or damage arising from the interpretation or use of the information, or reliance upon views contained in this report.